According to IUPAC nomenclature sodium nitroprusside is named as:

Sodium nitroprusside $$\mathrm{Na}_2\left[\mathrm{Fe}\left(\mathrm{CN}_5\right) \mathrm{NO}\right]$$ Let oxidation state of $\mathrm{Fe}$ is $x$ in this compound. \begin{aligned} & +2+x+(-1) 5+1=0 \\ & \text{ or }+2+x-5+1=0 \text{ or } x=+2 \end{aligned} Thus IUPAC name of sodium nitroprusside is sodium pentacyanonitrosyl ferrate (II)